It is known from the submitted Polish P-343136 invention titled non-return valve with a ball closing element, whose body is equipped with a through-channel together with an inlet and outlet terminated With a ring seat, on which the closing ball element is settled in the closing position, as well as it is equipped with a deflected channel, whose diameter is greater than the diameter of
the closing ball element, which it enters while the valve is in open position. By the inlet, in the place of junction between the deflected channel and the through-channel, the body has an extended flow cross-section. The valve deflected channel has a blind with a through hole connected with the outlet of the through-channel,settling the closing ball element in a fully open position, while the through-channel is in a form of an elbow or knee. This valve can be produced in three basic versions with respect to the fixing point of the blind with the through hole. The blind can be permanently fixed to the elbow-shaped guiding rail of the cover or of the cleaningcover or to the deflected channel of the valve body. In the invention known from the submitted Polish patent application P-343137, the non-return valves with a ball-shaped body have some improvements in form of a resistance seat made of an unfinished ring or in a form of two incomplete ring crescents. The idea of these valves is essentially based upon tight separation of the lower pressure section on the upper side of deflected area, which prevents liquid flow through the deflected channel at fully open position of the valve, reducing the flow resistance coefficient of the ball at it fully open position.